Mr.Tulkinghorn knows that very well.
But they are not all like the woman who now leaves him and his house behind, between whose plain dress and her refined manner there is something exceedingly inconsistent.

She should be an upper servant by her attire, yet in her air and step, though both are hurried and assumed--as far as she can assume in the muddy streets, which she treads with an unaccustomed foot--she is a lady.

Her face is veiled, and still she sufficiently betrays herself to make more than one of those who pass her look round sharply.
She never turns her head.

Lady or servant, she has a purpose in her and can follow it.

She never turns her head until she comes to the crossing where Jo plies with his broom.